But I suspect "art" media can be all over the map. Both BC and Epson have been making slip-stream changes in their gloss canvases, mostly to the surfaces and substrates but I think also to the emulsion formulations. While that was going on I was printing for holiday season stock, and I can see differences in prints made over the various batches, from the same profiles. I made a few different profiles during those changes, but won't post graphs because my i1Pro puck does not like measuring glossy canvas and there are probably large instrumental errors involved. I have been using the "prettiest" profiles I have for each canvas, rather than the ones I think might be more accurate but less warm and fuzzy.

I'm going to assume old warhorses like the many RC glossy and satin papers are rock stable by comparison.

I used to regard Epson media as the world's most consistent. But I suspect they may have changed their manufacturing strategy towards farming out fabrication to plants local to distribution centers, rather than in centralized production plants usually offshore to the consuming market, as before.

For instance the Epson Exhibition Gloss Canvas I have been receiving recently is unmistakably manufactured by the same plant that makes BC's Crystalline and other products. I think it's in Southern California. Same exact packaging, same cardboard tubes, same manufacturing code system on the same Avery labels, even the exact same substrate material, and unfortunately the exact same chronic manufacturing defects! All that's different is the emulsion. I think there's another thread here from a guy in Poland with a bad roll of Epson EHM. Just lower quality than I have previously seen from Epson products. The fundamental problem with all farm-out manufacturing is that it invites bidding, which invites low-balling, which invites production short cuts. Or maybe I'm just getting old and crotchety.

I can't speak to the other Epson canvas, but so far as Exhibition Canvas Matte is concerned, we've seen nothing but changes from lot to lot throughout 2012. Not only are there obvious physical differences in the canvas itself, there are enormous differences in end-to-end performance. At this point, we re-profile every production lot.

On a typical busy inkjet printer, what would be a normal time that you might re-profile the same ink and paper?

With the Canon IPF's, unless the paper changes you shouldn't ever need to re-profile. Just run the hardware calibration periodically (3-4 times a year for me, maybe a little more often for heavy-volume printing).

Process control is a procedure I encourage my clients to implement. By regularly printing an evaluation image and comparing them to a "reference print" made immediately after calibration and profiling will allow one to get a feel for how a device changes over time. Despite some evangelical promises, all inkjet printers drift over time and will need either re-calibration or re-profiling (if re-calibration isn't possible). HP and Canon large format inkjet printers have a built-in calibration procedure that, if followed, allows the user to use one profile for the life of the printer. Epson inkjets are very stable for low volume users and often don't require recalibration or re-profiling. However, one thing I've noticed with my high volume clients is that Epson's really do change a lot under high usage and do require re-calibration or re-profiling (the later being the easier option for some users). Under heavy use, you'll notice that evaluation prints off an Epson get darker and the shadow details start to plug up. One can recalibrate in a RIP or Colorbase or simply make a fresh round of profiles. I'm finding it smart for my high volume Epson users to do so once a year (or twice if they are really picky). I'm finding that low and high volume Canon iPF users should recalibrate twice a year or immediately after any parts replacements. It's just so easy to run the procedure on these printers that it's important to take advantage of it.

Silver halide machines are much more volatile and need recalibration anywhere from every 8 hours to once a week, depending on the machine and the users level of pickyness. Again, implementing a process control procedure takes the mystery out of what's happening and allows the user to visually see what's happening and make an educated decision as to how often they should take the time to re-calibrate.

With process control one can profile once, and calibrate often to maintain consistency. For those that don’t like the thought of process control, calibrating silver halide devices every 8 hours, HP and Canon inkjets twice a year, Epson inkjets once a year for high volume and Epson inkjets every 3 years for lower volume usage are decent rules of thumb, IMO.

I take it people don't feel there's any need to re-profile when they replace an ink cart?

No. Unlike silver halide chemistry which changes over time and with temperature exposure, inkjet ink is incredibly stable and manufactured with super tight consistency. Head replacements (from all brands - even Epson) however, do call for immediate re-calibration.

I take it people don't feel there's any need to re-profile when they replace an ink cart?

I've actually let the ink run out mid print, replaced a cart and the printer finished, no trace of where the old cart and new cart met. That is on Epson with their inks and papers. Outside of that YMMV.

I've actually let the ink run out mid print, replaced a cart and the printer finished, no trace of where the old cart and new cart met. That is on Epson with their inks and papers. Outside of that YMMV.

I'm sure you can appreciate how different this observation is from what was asked. When your print continued, it was still using the ink from the previous cartridge. Once the ink from the new cartridge flows down the tubes and into the heads and on the paper, I'd submit that it's indistinguishable from the previous cartridge (as long as it's from the same manufacturer and not very out of date).

When your print continued, it was still using the ink from the previous cartridge. Once the ink from the new cartridge flows down the tubes and into the heads and on the paper, I'd submit that it's indistinguishable from the previous cartridge (as long as it's from the same manufacturer and not very out of date).

Good point and yes, the ink hitting the print after cart change was from previous cart albeit, this was an Epson 2200 and there isn't a lot of ink in those tubes. With say a 9800, probably more ink than in the entire 2200 cart. And yes, I'd agree it's indistinguishable from the previous cart, at least those inks from Epson.